Study On The Requirement Of Metabolizable Glucose For8to10-month-old Holstein Heifers

Heifer herd is very important for development of dairy production. Proper rearing of heifer can not only increase the milk production, reduce the cost of rearing. The paper is focus on influence of daietary metabolizable glucose (MG) level on productive performance of heifer. A optimal MG level for8to10-month-old Holstein heifers was determined. This study will provide fundamental data to make feeding protocols and management strategies in breeding heifers.In Experiment1, propionic acid yield from the conventional feedstuffs was determined by in vitro. Five heifers were used for sampling rumen fluid through mouth using a stomach-tube. The POEG values from the common-used feeds for dairy cows were calculated according to the absorption rate of propionic acid through the regression models of propionic acid production and absorption of sheep given by Han Fei(2001).In Experiment2, Two cows fitted with permanent rumen cannulas were used for taking rumen fliud samples and feeds ruminal degradation test. The amount and degradability of the rumen bypass starch of the common-used feedstuffs for dairy cows and their degradation rates were determined by Nylon bag technique. And the rumen bypass starch of coin, soybean meal and wheat bran were420.29g/kg,63.99g/kg and200.61g/kg.In Experiment3, the digestibility of the rumen undegraded residue of corn were determined by freeze-dried intestine fluids from dairy cattle (FID). The most suitable condition of determining the digestibility of the corn starch residue in the small intestine by FID was0.4g FID to0.5g undegraded residue, and the optimal fermentation time was16hours. The digestibility of the rumen bypass starch of coin, soybean meal and wheat bran in small intestine were42.38%,33.13%,13.89%, respectively. According to the results of the experiment1and experiment2, experiment1the MG of coin, soybean meal, wheat bran, chinensis and corn silage for dairy cows were255.96g/kg,82.20g/kg,94.51g/kg,44.64g/kg、56.88g/kg, respectively.In Experiment4, this study was conducted to evaluate the dietary MG levels on growth performance, blood biochemical indicators and nutrients digestion of8to10-month-old Holstein heifers. Twenty-four Holstein heifers (292±22.05kg of BW) were divided into4groups in a randomized experiment design with the treatment period of60d. Animals were fed different diets in which MG levels were86(group A),100(group B),114(group C) and127(group D) g/kg respectively. Two periods digestive trials were carried out by AIA method, and feacal samples were collected from21to25days and from51to55days. The results obtained as follows:1) The average daily gain (ADG) was improved with the increasing of the levels of MG remarkably, and then tended to stable state. The ADG of each group were0.49,0.71,0.87and0.86g/kg, the ADG of group A was significantly lower than that in group C (P<0.05), there were no significant differences between group C and group D.2) The growth curve of all groups in8-10months did no differ among the treatments (P>0.05) and the apparent of nutrients digestibility were similar.3) The thirtieth and sixtieth day of the formal tests, BUN of group A was significantly higher than that in group C, the thirtieth day of the formal tests, INS of group B was significantly lower than that in group C. It is concluded that114g/kg level in diet could meet the MG needs of8-10-month-old Holstein heifers.